Lighting on triangles - every other one is darkish
The triangles are all being displayed in 'Shade Flat' mode, which is the default. To change this, go to edit mode and select all faces (hit 'A' once or twice, until all triangles are selected). Then Hit 'W' then select 'Shade Smooth'

[Shade Flat] mode is appropriate for modeling a faceted gemstone, or cut crystal glass, for example. Since blender cannot know ahead of time what type of shading you need, it defaults to 'Shade Flat'.